A case study of resistance factors for bearing capacity of shallow foundations using plate load test data in Korea

ABSTRACT

Ground conditions comprised of slightly or completely weathered rock are frequently encountered in design of bridge foundations in Korea. It is rather challenging to assess the accuracy of the common design methodologies for shallow foundations in these ground conditions as the foundation bearing capacity depends on the degree of weathering. This paper presents reliability-based derivation of resistance factors for the bearing capacity of shallow foundations on slightly and completely weathered rock using field plate load test data. More than 140 plate load tests were performed at 52 sites, 33 of which were considered to be of high quality and reliable. These high-quality tests were used to evaluate the uncertainties associated with the bearing capacity equations, and the resistance factors corresponding to current prescribed load factors. A reliability-based approach, with target annual failure probabilities of 1.0 × 10−3, 2.0 × 10−4, 1.0 × 10−4, was adopted to estimate the required resistance factors for different design equations. A Bayesian approach was adopted to facilitate quantification and propagation of statistical parameter uncertainty due to limited available data. The best estimates of the calibrated resistance factors range from 0.40 to about 0.47 for the considered target reliability levels, which is in good agreement with currently used values in Korea.

KEYWORDS:

• Bearing capacity
• shallow foundation
• resistance factor calibration
• weathered rock
• plate load test
• Bayesian methods

Acknowledgements

This study was performed under a research contract between Norwegian Geotechnical Institute (NGI) and Korea Institute of Civil engineering and building Technology (KICT) in connection with the project of “Development of Reliability-Based Design for Substructures of Cable Stayed Bridge”.

Additional information

Funding

The authors would like to acknowledge the financial support (Ministry of Land, Infrastructure and Transport of Korean government, Grant number: 21SCIPB119947-06) and the collected field plate load test data provided by KICT.